Color Harmony and the
Opponent-Process Channel
Theory
Christina Lewis
Psych 159
TRICHROMATIC THEORY
Thomas Young and Hermann von Helmholtz, 18’th-19’th century
Opponent-Process
Theory
• 1878 Ewald Hering
• Certain color combinations
don’t exist (we never see
them), such as reddish-green or
yellowish-blue
• Three receptor types, each with
opposing pairs: red green, blue
yellow, black white
Opponent Neurons
• Excitatory response to some wavelengths
and inhibitory response to others
• Red-Green receptors cannot send
information about both colors at the
same time
• Responses to one color of an opponent
channel are antagonistic to those to the
other color.
**More efficient, given that for the cones,
responses to certain wavelengths overlap.
Differences are more important.
CONES  BIPOLAR CELLS  GANGLION CELLS
PARVOCELLULAR
Processes differences between L & M
Cones, Red – Green differences
MAGNOCELLULAR
Processes difference between S
cones, blue-yellow differences
Intensity of light
How it Works
• Red-Green Channel: The difference
between long-wavelength and
middle-wavelength cone signals.
• Yellow-Blue Channel: The
difference between short
wavelength cones and the sum of
the other two cones.
• *Luminance Channel*: Based on
inputs from all the colors. Detects
the difference in brightness of color
information.
ISOLUMINANCE
DIFFERENT COLORS - SAME BRIGHTNESS
This is a very bad words-on-background color-pair, because
there is very little difference between the luminance of the
color dark-blue and the luminance of the color black.
Youhellohavepsychnoclassproblemthisreadingisonly
athereadinggreentestwords.
BAD BAD BAD DON’T DO THIS IN YOUR
FUTURE POWERPOINTS
Implications
• Color-opponent channels:
• Color is good for SEPARATING OBJECTS
• Separating regions
• Luminance Channel:
• Contrast transmits SHAPE INFORMATION
(**edges**)
• Fine detail
Other Important Properties of Opponent Channels
• Luminance > Purely Chromatic Information:
• (for many aspects of vision including):
• Stereoscopic depth: Cannot detect differences in depth based purely on color channel
information
Other Important Properties of Color Channels
• Motion Perception:
• Luminance > Purely Chromatic Information
• If gratings of different colors but equal luminance are moving, we detect the
speed much slower (or for some humans, completely immobile) as compared
to a grating of very large contrast difference (for example a black and white
or black and yellow grating).
After-Images
-Fatigue of one color receptive causes stimulation of its
opponent color in the pair